Multicolor, multilayer photographic elements are well known in the art. Such materials generally have three different selectively sensitized silver halide emulsion layers coated on one side of a single support. Each layer has components useful for forming a particular color in an image. Typically, the materials utilize color forming couplers or dyes in the sensitized layers during processing.
One commercially important process intended for use with color reversal photographic films useful for providing positive color images, can include the following sequence of steps: first (or black-and-white) development, washing, reversal re-exposure, color development, bleaching, fixing, and washing and/or stabilizing. Another useful process is similar but includes stabilizing between color development and bleaching. Such conventional steps are described, for example, in U.S. Pat. No. 4,921,779 (Cullinan et al), U.S. Pat. No. 4,975,356 (Cullinan et al), U.S. Pat. No. 5,037,725 (Cullinan et al), U.S. Pat. No. 5,523,195 (Darmon et al) and U.S. Pat. No. 5,552,264 (Cullinan et al).
Thus, it is known that after the first development, the exposed films are subjected to a reversal re-exposure and subsequent color development. Certain nucleating agents have been used in a solution applied after the first development in place of reversal re-exposure. Such a solution is known as a "reversal bath". Very early reversal baths contained certain boron compounds as nucleating agents, but they had a number of disadvantages that led to improvements with the use of stannous salts that are stable in both acidic and alkaline environments.
The nucleating agents in the reversal bath are intended to reduce silver ion remaining undeveloped from the first development step. Commercial reversal baths generally contain stannous ion as the silver ion reducing agent, as described for example, in U.S. Pat. No. 3,617,282 (Bard et al). Stannous ion is generally provided in the form of a simple or chelated salt.
Commercial reversal bath solutions, however, can exhibit a number of problems. They may give off an unpleasant odor due to the presence of volatile organic acids typically used as buffers, and undesirable biogrowth may occur in the processing tank. In addition, reversal bath solutions may require filtration after certain hours of use because of the build-up of predominately organic precipitates from high biological matter. Control of such visible or malodorous biogrowth is a considerable challenge in the art. This would reduce the need for filtration, filter changes and other costly maintenance.
The microbial population in most commercial "seasoned" or used reversal bath solutions is commonly on the order of 10.sup.4 to 10.sup.5 CFU/ml (colony forming units/ml). Visible accumulation of these populations causes customer dissatisfaction because of the need for more frequent solution replacement and processor tank cleaning. Thus, there is a need to reduce the visible level of biogrowth in such solutions.
Although there are many known microbial control agents, in order to use them effectively in photographic processing solutions, interactions with components of the processed photographic materials must be avoided. In addition, the microbial control agents must not interact with other components of the processing solutions.
Previous attempts to solve this problem are described in U.S. Pat. No. 5,811,225 (McGuckin et al) in which various quaternary ammonium compounds were used as microbial control agents at 50-150 ppm. The preferred microbial control agent in those embodiments was myristyltrimethyl ammonium bromide (MTAB). However, when MTAB or other described compounds were used at the noted concentrations, they tended to react with components (for example, certain filter dyes) that leach out of some processed color reversal films. One reaction product produced is a bright pink precipitate that is unacceptable to customers, requiring costly maintenance and frequent solution replacement.
First of all, there is a need for a low cost reversal bath composition that is not susceptible to the problems noted above (for example visible biogrowth), and which continues to have the desirable photochemical properties obtained from the use of stannous ion. Preferably, there is a need for a reversal bath composition that does not contain any precipitates from reaction of the microbial control agents with process film components.